Method of preparing viscose rayon



United States Patent Cfific 2,898,182 Patented Aug. 4, 1959 2,892,182METHODOF PREPARING VISCOSE RAYON Marion R. Lytton, West Chester, Pa.,assignor .to American Viscose Corporation, Philadelphia, Pa., a corpora-:tionof Delaware No Drawing. Application December 30, 1954 Serial No.478,940

6 Claims. (Cl. 18-54) This invention relates to the production of shapedbodies of regenerated cellulose from viscose and more particularly tofilaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regeneratedcellulose from viscose, a suitable cellulosic material such as purifiedcotton linters, wood pulp, mixtures thereof, and the like is firstconverted to an alkali cellulose by treatment with a caustic sodasolution and after shredding the treated cellulose material, it isallowed to age. The aged alkali cellulose is then converted to axanthate by treatment with carbon disulfide. The cellulose xanthate issubsequently dissolved in a causticsoda solution in an amount calculatedto providea viscose of the desired cellulose and alkali content. .Afterfiltration, the viscose solution is allowed to ripen and is subsequentlyextruded through a shaped orifice into a suitable coagulating andregenerating bath.

In the production of shaped bodies such as filaments, the viscosesolution is extruded through a spinneret into a coagulating 'andregenerating bath consisting or an aqueous acid solution containing zincsulfate. The filament may subsequently be passed through a, hot aqueousbath where it is stretched to improve its properties such as tensilestrength. The filament may then be passed through a dilute aqueoussolution of sulfuric acid and sodium sulfate to complete theregeneration of the cellulose, in case it is not completely regeneratedupon leaving the stretching stage. The filamentis' subsequentlysubjected to washing, purification, bleaching, possibly other treatingoperations and drying, being collected either before or after thesetreatments.

The filaments as formed by the conventional methods, consist of a skinor outer shell portion and a core portion with a sharp line ofdemarkation between the two. The cross-section of the filaments exhibitsa very irregular or crenulated exterior surface when even small amountsof zinc salts or certain other polyvalent metal salts are present in thespinning bath. The skin and core portions of the filament representdifferences in structure and these different portions possess differentswelling and staining characteristics, the latter permitting a readyidentification of skin and core. The sharply irregular and crenulatedsurface structure has a relatively low abrasion resistance and readilypicks up foreign particles such. as dirt. Although the core portionpossesses a relatively high'tensile strength, it has a low abrasionresistance and a low flex-life, is subject to fibrillation and isrelatively stiff.

It has now been discovered that the presence of small amounts of certainalkali-soluble alkylene oxide adducts of N-fatty alkyl or N-aliphaticalanine (aminopropionic acid) in viscose results in the production ofshaped bodies of regenerated cellulose such as filaments, films, sheetsand the like composed of all skin and having improved properties andcharacteristics providing that the amount of the alkylene oxide adductis maintained with conveniently added to viscose in-the 2 certain limitsand the composition of the spinning bath is maintained within certaincomposition limits which Will be defined hereinafter. The most readilydistinguishable characteristics as compared to conventional filamentsinclude a smooth, non-crenulated surface and the filaments consistentirely of skin.

The alkylene oxide adduct utilized in the modification of the viscosemay bean adduct of either the alpha or beta forms of N-fatty alkylorN-aliphatic alanine. The fatty alkyl group or aliphatic radical is astraighthydrocarbon chain containing from 6 to 24 carbon atoms and-maybe saturated or unsaturated. Theradical may be obtained from the fattyacids derived from animal and vegetable fats and oils such as coconutoil, cottonseedoil, corn oil, soya bean oil, palm oils, peanut oil,tallow and the likeand the hydrogenated fats and oils. These alaninederivatives asutilized for the purposes of thisinvention may be purecompounds wherein a relatively .pure aliphatic radical, such as a laurylradical, is employed in preparing the adduct, orthe N-aliphatic alaninemay consist ofamixture of compounds where the aliphatic radicals oftheindividual compounds are obtained from a mixture of fatty acidsof aparticular fat or oil such as coconut oil. The adducts may be preparedby reacting a N-aliphatic, alanine, or a mixture of N- aliphaticalanines with an alkylene oxide or a polyoxyalkylene glycol. Adductswhich aresatisfactory for the purposes of this inventionmaybe derivedfrom capric, lauric, myristic, oleic, stearic acids and like acids orfron-r a mixture of fatty acids such as obtained from coconut oilorother fat or oil. The compounds may be form of solutions in alkali orin water.

This invention contemplates the use of alkylene oxide adducts of N-fattyalkyl or N-aliphatic alanines having from about-8 to about 30 or morealkyleneoxide units per molecule, preferably between about 12 and 20alkylene oxide-units per molecule of the N-aliphatic'alanine. It'isobvious that for all practical purposes considering cost, ease ofpreparation-, commercia'l availability and solubility in waterandinalkali-solutions, the ethylene oxide adducts are preferred. For purposesof illustration only, the invention is described by reference to theethylene oxide adducts but it is to be understood that other alkyleneoxide adducts such as propylene oxide adducts are equally satisfactoryso long as they possess the required solubility. That is, the adductmust have sufficient solubility to permit a minimum amount of the adductto be dissolved in the viscose. Commercial materials of this type suchas the substance marketed as Good-Rite CEA are entirely satisfactory.This substance is a reaction product of ethylene oxide and a mixture ofN-aliphatic alanines wherein the aliphatic radicals of the individualalanines are obtained from coconut oil and has an average of about 15ethylene oxide units per molecule of the N-fatty alkyl alanine. v

. The term adduct is used herein to simplify the disc'losureanddescription and designates the reaction products formed by the reactionof an alkylene oxide or a polyoxyalkylene glycol with an N-fatty alkyl,alanine .or a-mixture of N-fatty alkyl alanines wherein the polyofanaline being within the stated range, are satisfactory.

These alkali-soluble adducts may be represented by the followingstructural formulas, the first representing 3 the adducts of the alphaform of alanine and the second representing the adducts of the beta formof alanine wherein R is an aliphatic radical or straight carbon chain offrom 6 to 24 carbon atoms, at is 2 or 3 and m is from about 8 to about30, preferably from 12 to 20.

The amount of the adduct or modifier which is incorporated in theviscose must be at least about 0.5 by weight of the cellulose in theviscose and may vary up to about 4%, preferably, the amount varies from0.5% to 2.5%. Lesser amounts do not result in the production of productsconsisting entirely of skin and greater amounts affect adversely thephysical properties of the products. Amounts within the preferred rangeare most effective in enhancing the characteristics and properties ofthe products. The adduct may be added at any desired stage in theproduction of the viscose such as in the preparation of the refined woodpulp for the manufacture of viscose, before or during the shredding ofthe alkali cellulose, to the xanthated cellulose while it is beingdissolved in the caustic solution or to the viscose solution before orafter filtration. The adduct is preferably added after the cellulosexanthate has been dissolved in the caustic solution and prior tofiltration.

The viscose may contain from about 6% to about 8% cellulose, theparticular source of the cellulose being selected for the ultimate useof the regenerated cellulose product. The caustic soda content may befrom about 4% to about 8% and the carbon disulfide content may be fromabout 30% to about 50% based upon the ning bath be maintained within awell defined range.

The presence of the alkylene oxide adduct in the viscose combined withthese limited spinning baths results in the production of yarns ofimproved properties such as high tenacity, high abrasion resistance,high fatigue re- The acid content of the spinning bath is balancedagainst the composition of the viscose. The lower limit of the acidconcentration, as is well known in the art, is just above the slubbingpoint, that is, the concentration at which small slubs of uncoagulatedviscose appear in the strand as it leaves the spinning bath. Forcommercial operations, the acid concentration of the spinning bath isgenerally maintained about 0.4% to 0.5% above the slubbing point. Forany specific viscose composition, the acid concentration of the spinningbath must be maintained above the slubbing point and below the point atwhich the neutralization of the caustic of the viscose is suflicientlyrapid to form a filament having a skin and core.

. tion of the spinning baths which are satisfactory for the productionof the all skin products from a 7% cellulose, 6% caustic-viscose andcontaining the alkylene oxide adducts lies between about 5% and about8%. The acid concentration may be increased as the amount of thederivative is increased and also as the salt test of sistance andconsisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is alow acid-high zinc spinning bath containing from about 10% to about 25%sodium sulfate and from about 3% to about 15% Zinc sulfate, preferablyfrom 15 to 22% sodium sulfate and from 4% to 9% zinc sulfate. Othermetal sulfates such as iron, manganese, nickel and the like may bepresent and may replace some of the zinc sulfate. The temperature of thespinning bath may vary from about 25 C. to about 80 0, preferablybetween about 45 C. and about 70 C. In the production of the all skintype filaments, the temperature of the spinning bath is not critical,however, as is well known in the conventional practice in the art,certain of the physical properties such as tensile strength varydirectly with the temperature of the spinning'bath. Thus, in theproduction of filaments for tire cord purposes in accordance with themethod of this invention, the spinning bath is preferably maintained ata temperature between about C. and 65 C. so as to obtain the desiredhigh tensile strength.

the viscose is increased. There is an upper limit, however, for the acidconcentration based upon the amount of adduct and the concentration ofcaustic in the viscose. All skin products cannot be obtained if the acidconcentration is increased above the maximum value although the amountof the alkylene oxide adduct is increased beyond about 4% while otherconditions are mantained constant. Increasing the caustic soda contentof the viscose beyond about 8% is uneconomical for commercial productionmethods. For example, a viscose containing about 7% cellulose, about 6%caustic soda, about 41% (based on the weight of cellulose) carbondisulfide, and 2% (based on the weight of cellulose) of an ethyleneoxide adduct of a mixture of N-aliphatic alanines, as described, inwhich the aliphatic radicals of the individual alanines are obtainedfrom the fatty acids of coconut oil and having about 15 ethylene oxideunits per molecule, and having a salt test of about 9.5 when extrudedinto spinning baths containing 16 to 20% sodium sulfate, 4 to 8% zincsulfate and sulfuric acid not more than about 8% results in theproduction of all skin filaments. Lesser amounts of sulfuric acid may beemployed. Greater amounts of sulfuric acid result in the production ofproducts having skin and core. A lowering of the amount of the adduct,the lowering of the caustic soda content or the lowering of the salttest of the viscose reduces the maximum permissible acid concentrationfor the production of all skin filaments. Ithas been determined that themaximum concentration of acid which is permissible for the production ofall skin products is about 8.5%.

The presence of the adducts in the viscose retards the coagulation and,therefore, the amount of adduct employed must be reduced at highspinning speeds. Thus,

for optimum physical characteristics of an all skin yarn formed from aviscose as above and at a spinning speed of about 50 meters per minute,the adduct is employed in amounts within the lower portion of the range,for example, about 0.6% to 0.75%. The determination of the specificmaximum and optimum concentration of acid for any specific viscose,spinning bath and spinning speed is a matter of simple experimentationfor those skilled in the art. The extruded viscose must, of course, beimmersed or maintained in the spinning bath for a period sufiicient toeffect relatively complete coagulation of the viscose, that is, thecoagulation must be sufficient so that the filaments will not adhere toeach other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication .oftire cord, the filaments are preferably stretched after removal from theinitial coagulating and regenerating bath. From the initial spinningbath, the filaments may be passed through a hot aqueous bath which mayconsist of hot water or a dilute acid solution and may be stretched fromabout 70% to about 120%, preferably between 85% and 100%. Yarns forother textile purposes may be stretched as low as The precise amount ofstretching will be dependent upon the desired tenacity and otherproperties and the specific type of product being produced. If desired,the filaments may be stretched in air. It is to be understod that theinvention is not restricted to the production of filaments and yarns butit is also applicable to other shaped bodies such as sheets, films,tubes and the like. The filaments may then be passed through a finalregenerating bath which may contain from about 1% to about 5% sulfuricacid and from about 1% to about 5% sodium sulfate with or without smallamounts of zinc sulfate if regeneration has not previously beencompleted.

The treatment following the final regenerating bath, or the stretchingoperation where regeneration has been completed, may consist of awashing step, a desulfurizin'g step, the application of' a finishing orplasticizing material and drying before or after collecting, or mayinclude other desired and conventional steps such as bleaching and thelike. The treatment after regeneration will be dictated by the specifictype of shaped'body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing thesmall amounts of the alkylene oxide adducts and spun in the spinningbaths of limited acid content have a smooth or non-crenulated surfaceand consist substantially entirely of skin. Because of the uniformity ofstructure throughout the filament, the swelling and stainingcharacteristics are uniform throughout the crosssection of the filament.Filaments produced pursuant to this invention and consisting entirely ofskin have a high toughness and a greater flexing life than filaments asproduced according to prior methods which may be attributedby'theuniformity in skin structure throughout the filament. Although thetwisting of conventional filaments, as in the production of tire cord,results in an appreciable loss of tensile strength, there is appreciablyless less in tensile strength in the production of twisted cords fromthe filaments consisting entirely of skin. Filaments prepared fromviscose containing the alkylene oxide adducts have a high tensilestrength as compared to normal regenerated cellulose filaments, havesuperior abrasion and fatigue resistance characteristics and have a highflex-life. Such filaments are highly satisfactory for the production ofcords for the reinforcement of rubber products such as pneumatic tirecasings, but the filaments are not restricted to such uses and may beused for other textile applications.

The invention may be illustrated by reference to the preparation ofregenerated cellulose filaments from a viscose containing about 7.4%cellulose, about 6.3% caustic soda, and having a total carbon disulfidecontent of about 41% based on the weight of the cellulose. The viscosesolutions were prepared by xanthating alkali cellulose by theintroduction of 36% carbon disulfide based on the weight of thecellulose and churning for about 2% hours. The cellulose xanthate wasthen dissolved in caustic sodasolution. An additional 5% carbondisulfide was then added to the mixer and the mass mixed for about onehour. The desired amount of the ethylene oxide adduct of N-aliphaticalanine was added to the solution and mixed for about /2 hour. Theviscose was then allowed to ripen for about 30 hours at 18 C.

Example '1 uApproximately 1% (based on the weight of the cellulose) ofan ethylene oxide adduct of N-fatty alkyl alanine (fatty alkyl groupsfrom coconut oil) known as Good-Rite CEA was added to and incorporatedin the viscose as described above. The viscose employed in the '6spinning of filaments had a salt test of 9.4. The viscose was extrudedthrough a spinneret to form a 208 denier, 120 filament yarn at a rate ofabout 22 meters per minute. The coagulating and regenerating bath wasmaintained at a temperature of about 60 C. and contained 7.8% sulfuricacid, 8% zinc sulfate and 17% sodium sulfate. The yarn was stretchedabout 82% while passing through a hot water bath at 95 C. The yarn wascollected in a spinning box, washed free of acids and salts and dried. IThe individual filaments have a smooth, non-crenulated exterior surfaceand consist entirely of skin, no core being detectable at highmagnification (etg. l500 The filaments of a control yarn spun with thesame viscose but without the addition of the modified agent and 'spununder the same conditions, exhibit a very irregular and serrated surfaceand are composed of about skin and the balance core with a sharp line ofdemarkation between the skin and core. Other physical properties are setforth in the table which follows the examples.

Example 2 To a viscose as described above, there was added 2% of thesame ethylene oxide adduct (Good-Rite CEA). The viscose had a salt testof 9.4 and was spun into a 202 denier, 120 filament yarn by extrusioninto a spinning bath containing 7.8% sulfuric acid, 8% zinc sulfate, and17% sodium sulfate. The bath was maintained at 60 C. and the extrusionrate was about 43 meters per minute. The filaments were subsequentlypassed through a hot water bath at C. and stretched about 74%. The yarnwas collected in a spinning box, washed free of acids and salts anddried.

The individual filaments were readily distinguishable from controlfilaments in that they have a smooth, noncrenulated surface and consistentirely of skin while the control filaments have a very irregular andserrated surface and consist of about 80% skin and the balance core witha sharp line of demarkation between the skin and core. Other physicalproperties are set forth in the table which follows the examples.

Example 3 To a viscose solution as described above, there was added 2%of the same ethylene oxide adduct of N-aliphatic alanine wherein the.aliphatic radical was derived from coconut oil and contained about 15ethylene oxide units perntolecule, Good-Rite CEA. The viscose had a salttest of 9.8 and was spun into a 224'denier, filament yarn by extrusioninto a bath containing 7.4% sulfuric acid, 8% zinc sulfate and 17%sodium sulfate. The bath was maintained at a temperature of 60 C. Theextrusion rate was about 22 meters per minute. The water bath wasmaintained at about 95 C. and the filaments were stretched approximately82% while passing throughthe hot water. The yarn was collected in aspinning box, washed free of acid and salts and dried.

The individual filaments were readily distinguishable from controlfilaments prepared from viscose containing no modifier in that they havea smooth, non-crenulated surface and consist entirely of skin. Controlfilaments have a very irregular and serrated surface and consist ofabout 85% skin and the balance core with a sharp line of demarkationbetween the skin and core. Other physical properties are set forth inthe table which follows the examples.

Example 4 As a control for the foregoing examples, a viscose solution,prepared as described above, havinga salt test of 9.7 was spun into a210 denier, 120 filament yarn by extrusion into a bath containing 7.5%sulfuric acid, 8%. zinc sulfate and 19% sodium sulfate. The bath wasmaintained at a temperature of about 60 C. The extrusion rate was about22 metersper minute. The water bath was maintained at a temperature ofabout 95. C. and the filaments were stretched 82% While passing throughthe hot water. The yarn was-collected in a spinning box, washed free ofacid and salts and dnied.

The individual filaments have a very irregular and serrated surface andconsist of about 85% skin and the balance core with a sharp line ofdemarkation between the skin and the core. Other characteristics are setforth in the table which follows:

Tenacity, Grams per Elongation,

denier percent Skin,

percent Wet Dry Wet Dry Example 1 2. 3. 3 26 21 100 Example 2 1. 5 2. 322 21 100 Example 3 3.0 2. 2 27 21 100 Example 4 (Control) 2.2 3. 2 2621 85 Although the tenacity and elongation are the only properties setforth, they have been chosen because of the ease and simplicity withwhich such properties may be determined. In some instances, productsmade in accordance with this invention do not exhibit improvements intenacity and elongation, however, the products consist of asmooth-surfaced, all skin structure and possess improved abrasionresistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is itsrelatively high cross-sectional swelling when Wet with water, thisswelling amounting to fromabout 65% to about 80% for rayon produced bycom ventional methods. Rayon filaments produced in accordance with themethod of this invention have an appreciably lower cross-sectionalswelling characteristic, the swelling amounting to from about 45% toabout 60%.

The alkylene oxide adducts may be added to any desired viscose such asthose normally used in industry, the specific viscose composition setforth above, being merely for illustrative purposes. The adducts may beadded at any desired stage in the production of the viscose and may bepresent in the cellulosic raw material although it may be necessary toadjust the amount present to produce a viscose having the properproportions of the adduct at the time of spinning.

The term skin is employed to designate that portion of regeneratedcellulose filaments which is permanently stained or dyed by thefollowing procedure: A microtome section of one or more of the filamentsmounted in a wax block is taken and mounted on a slide with Meyersalbumin fixative. After dewaxing in xylene, the section is placed insuccessive baths of 60% and 30% alcohol for a few moments each, and itis then stained in 2% aqueous solution of Victoria Blue BS conc.(General Dyestuffs Corp.) for l to 2 hours. At this point, the entiresection is blue. By rinsing the section first in distilled water andthen in one or more baths composed of water and 90% dioxane for a periodvarying from 5 to 30 minutes depending on the particular filament, thedye is entirely removed from the core, leaving it restricted to the skinareas.

While preferred embodiments of the invention have been disclosed, thedescription is intended to be illustrative and it is to be understoodthat changes and variations may be made without departing from.- thespirit and scope of the invention as defined by the appended claims.

I claim:

1. In a method of producing shaped bodies of regenerated celluloseconsisting substantially entirely of skin, the step which comprisesextruding viscose containing from about 0.5% to about 4%, based on theweight of the cellulose in the viscose, of a modifying agent into anaqueous spinning bath containing from about 10% to-25% sodium sulfate,from about 3% to zinc sulfate and sulfuric acid, the sulfuric acidcontent of'the spinning bath exceeding the slubbing point but not exceeding about 8.5%, the modifying agent being a substance selected fromalkali-soluble compounds corresponding to the formulas R COOH andmixtures of such compounds, wherein R is an aliphatic radical havingfrom 6 to 24 carbon atoms, x is a whole number at least 2 but not morethan 3 and m is from about 8 to about 30. l

2. The step in the method as defined in claim 1 wherein the modifyingagent is selected from the compounds and mixtures of compoundscorresponding to the formulas as set forth in claim 1 when x is 2.

3. The step in the method as defined in claim 1 wherein the modifyingagent is a mixture of compounds corresponding to the formulas as setforth in claim 1 when R of the individual compounds represents thealiphatic radicals derived from the fatty acids of coconut oil and x is2.

4. The method of producing shaped bodies of regenerated celluloseconsisting substantially entirely of skin which comprises adding to andincorporating in viscose from about 0.5% to about 4%, based on theweight of the cellulose in the viscose, of a modifying agent andextruding the viscose into an aqueous spinning bath containing fromabout 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate andsulfuric acid, the sulfuric acid content of the bath exceeding theslubbing point but not exceeding about 8.5%, the modifying agent being asubstance selected from alkali-soluble compounds corresponding to theformulas 'R ('10 OBI /N--(I7H H(O:H2z0)m CH3 and N-OH2CH2COOH H(CZH2Z )Mand mixtures of such compounds, wherein R is an aliphatic radical havingfrom 6 to 24 carbon atoms, x is a whole number at least 2 but not morethan 3 and m is from about 8 to about 30.

5. The method as defined in claim 4 wherein the modifying agent is amixture of compounds corresponding to the formulas as set forth in claim4 when R of the individual compounds represents the aliphatic radicalsderived from the fatty acids of coconut oil.

6. The method of producing shaped bodies of regenerated celluloseconsisting substantially entirely of skin which comprises adding to andincorporating in a viscose from about 0.5% to about 2.5%, based on theweight of the cellulose in the viscose, of a modifying agent, ripeningthe viscose to a sodium chloride salt point of not less than 9 andextruding the viscose into an aqueous spinning bath containing fromabout 16% to 20% sodium sulfate,'fr'om about 4% to 9% zinc sulfate andsulfuric acid, the sulfuric acid content of the spinning bath exceedingthe slubbing point but not exceeding about 8.5%, the modifying agentbeing a mixture of substances corresponding to the formulas and whereinthe radicals R of the individual compounds are the aliphatic radicalsderived from the fatty acids of coconut oil and x is 2. 10

References Cited in the file of this patent UNITED STATES PATENTS

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSECONSISTING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEP WHICH COMPRISESEXTRUDING VISCOSE CONTAINING FROM ABOUT 0.5% TO ABOUT 4%, BASED ON THEWEIGHT OF THE CELLULOSE IN THE VISCOSE, OF A MODIFYING AGENT INTO ANAQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10% TO 25% SODIUM SULFATE.FROM ABOUT 3% TO 15% ZINC SULFATE AND SULFURIC ACID, THE SULDURIC ACIDCONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOTEXCEEDING ABOUT 8.5%, THE MODIFYING AGENT BEING A SUBSTANCE SELECTEDFROM ALKALI-SOLUBLE COMPOUNDS CORRESPONDING TO THE FORMULAS